The dead ball rule

[Peruvian]

Before the game we go over ground rules and the opposing coach said anything that passes by the fence(extended) in foul territory was a dead ball.

Was there a chalk line there signifying where the fence line extended should be? If not, I'd be hesitant to call the play dead unless it obviously crossed the line (with no chalk line, how can I be sure). Are you saying the ball crossed the line by several feet (making it obvious), or not far enough that the umpire could clearly tell?

To protect yourself in the future, put a chalk line down. We have several high schools here that have tarps in live ball territory that they don't want players to step on if they should make a play near it (funding issues). Several instances happened this year during pregame, when the coach says "They can lean on it, but they can't step on it. If they do, it's dead." I'd have to say, "not unless you make that a dead ball area, we have to play it live." Just like a media area in the field of play - if media are present, they have to stay in that designated, pre-drawn circle.

Keep this in mind, no ground rule can supercede a book rule.